1. Field of the Invention
The present invention relates to an ink jet cartridge having an ink tank portion and a print head portion which are integrally formed or coupled together so as to form one member.
2. Description of the Related Art
Examples of ink tanks for use in ink jet printing apparatuses include an ink jet cartridge having a print head. The ink jet cartridge has a print head portion 801 and an ink tank portion 802 which are integrally formed, for example, as shown in FIG. 9. The print head portion 801 has ejection ports 804 through which ink is ejected, and the ink tank portion 802 accommodates ink to be supplied to the print head portion 801. An absorber 803 impregnated with ink is housed in the ink tank portion 802. The absorber 803 is formed of a sponge or the like. The print head portion 801 and the ink tank portion 802 can be integrally installed on and removed from a holder in an ink jet printing apparatus.
If such an ink jet cartridge is adapted for color printing, the ink jet cartridge may need to eject, for example, at least three types of ink corresponding to at least three colors. In this case, in connection with the positions and arrangement of the ejection ports, formed in the print head portion, a manufacturing process is facilitated by forming all the ejection ports in as few semiconductor substrates as possible. This is because when the positional relationship among a plurality of nozzle rows corresponding to a plurality of colors is to be accurately established (on the order of microns), manufacturing can be achieved with the positional relationship among the nozzle rows maintained, by arranging all the color nozzles in one substrate. Thus, even when the nozzle rows correspond to the plurality of colors, the colors are unlikely to be misaligned upon impacting a print medium. This is why a scheme of arranging a plurality of colors on one semiconductor substrate has been adopted.
However, if a plurality of inks corresponding to a plurality of nozzles is provided in one print head portion with the ink tank and the print head formed as one member, the consumption of the ink may vary among the inks of the different colors. Thus, when ink of one color is exhausted in spite of sufficient amounts of inks of the other colors remaining, the ink jet cartridge housing the inks of all the colors needs to be changed.
In contrast, an ink jet cartridge is known which has separate print head portions for the respective colors and in which each of the print head portions is integrated with the corresponding ink tank portion. When the print head portions for the respective colors are provided as in the case of this ink jet cartridge, the ink of each color can be fully used up. The use efficiency of the inks is thus improved. This also reduces the amount of waste ink and thus adverse effects on the environment.
However, volume efficiency decreases, which is the rate of an ink accommodation volume in the volume of the whole ink jet cartridge. This increases the size of the ink jet cartridge relative to the size of other types of ink jet cartridges of the same ink capacity. According to the present inventors' examinations, with a scheme in which absorbers such as sponges are housed in the respective ink tank portions of the ink jet cartridge, usable ink amount is about 50% of the volume of the ink tank portion.
Furthermore, in the ink jet cartridge of this type, the absorbers not only hold the ink but also generate appropriate negative pressure in the ink reaching nozzles in the print head portion, on the basis of the capillary force of recesses and protrusions on the surface of each of the absorbers. The negative pressure is thus generated in the print head portion to prevent the ink from leaking from the print head portion except during printing. Further, there is another scheme of utilizing water head difference for ink jet printing apparatuses. However, with this scheme, the ink tanks need to be positioned higher than an ejection port surface on which the ejection ports are formed. Consequently, installing the ink jet cartridge, which this structure kept as it is on a carriage, is difficult. Furthermore, it is required that the ink is supplied through tubes from the ink tank portion to the print head portion. This complicates the structure and increases manufacturing costs.
Another scheme of generating negative pressure inside the print head is means for generating negative pressure using a mechanical regulator apparatus. However, it is technically difficult to accurately and continuously generate a negative pressure required for ink jet printing apparatuses (−100 Pa to −3000 Pa). This also increases the number of parts required and thus tends to increase costs. Furthermore, parts used to generate the negative pressure tend to be large, increasing the rate of the volume of these parts in the volume of the ink jet cartridge. This reduces the rate of the volume of the ink tank portion in which the ink is accommodated. Additionally, an ink storing portion needs to be provided which prevents ink from leaking from the print head portion even with a change in posture or environment.
Another scheme houses ink in a bag located inside a housing and formed of a flexible film. The scheme involves placing a spring inside the bag to adjust the pressure inside the bag while maintaining the shape of the bag, by means of the spring. The ink jet cartridge based on this scheme makes it possible to generate negative pressure in the ink storing portion while storing the ink in the ink storing portion. However, the ink jet cartridge based on this scheme increases the number of parts required and requires the delicate and flexible bag to allow to generate the negative pressure and to keep in a stable condition. The ink jet cartridge thus requires high manufacturing costs. The costs cannot be offset and the adoption of the ink jet cartridge based on this scheme is not advantageous, unless a printing apparatus using pigment inks which may precipitate or applied to any other special purpose is used. With the pigment ink, the pigment component of the ink precipitates to the bottom of the ink, requiring a mechanism for agitating the ink. The ink jet cartridge based on this scheme advantageously ensures a space in the ink storing section which is required to agitate the ink. Consequently, the precipitated pigment ink can be agitated before being ejected.
An example of means for solving these problems is an ink tank configured such that an absorber is housed in one space while ink is accommodated in the other space, with the spaces partitioned by a partition wall having a communication portion formed in a part thereof. The ink tank of this type is called a partially-absorber-stored-type. The amount of usable ink in this ink tank type is at least about 70% of the tank volume. The ink tank type thus has a relatively high volume efficiency.
FIG. 10 shows a form of a conventional ink tank 900 based on this scheme. An absorber 907 that absorbs and holds ink is housed in an absorber chamber 903. An atmospheric communicating port 905 through which open air is taken in is formed in a part of a wall surface of the absorber chamber 903 of the ink tank, which is located farther from the print head. A supply port 906 and a pressure contact member 908 are arranged in an area of the absorber chamber 903 which is closer to the print head. Ink is supplied to the print head through the supply port 906, and the pressure contact member 908 guides the ink from the absorber 907 to the vicinity of the supply port 906 for collection by means of a capillary force stronger than that of the absorber 907. The pressure contact member 908 has a function of passing the ink to a capillary part (for example, a high-density filter) located in an ink channel extending from the ink tank portion to the print head to take in the ink. With the ink tank 900 placed on the carriage, negative pressure can be generated by the capillary forces of the absorber 907 and the pressure contact member 908. This prevents the ink from leaking through the ejection ports.
With the ink tank 900, configured such that the absorber is housed in one space while the ink is accommodated in the other space, the ink can be stably supplied. The ink tank 900 also allows negative pressure to be generated inside the print head using a simple structure, reducing the number of the parts required. Consequently, the ink tank can be manufactured by reduced costs. This scheme is also advantageous in that the presence or remaining amount of ink can be checked by making a container as the ink storing portion 901 to be transparent and placing optical means, for example, a reflection prism 902, inside the container.
The ink tank based on this scheme has been examined by the present inventors and adopted for many commercially available ink tanks. However, attention needs to be paid to the form in distribution of the ink tank owing to the structure and nature thereof.
The ink tank 900 of this type is shipped after the ink storing portion 901 and the absorber chamber 903 have been filled with ink in a factory or the like. However, during distribution from shipment in the factory until delivery to users, the ink in the ink tank becomes unstable because of possible vibration during conveyance or a possible variation in atmospheric pressure or temperature during storage. As a result, the ink may leak to the exterior.
In particular, the flow of air from the absorber chamber 903 to the ink storing portion 901 results from, for example, a variation in the volume of ink caused by the repeated freezing and unfreezing of the ink. In this case, the ink flows in one direction, and when the flow occurs, the ink flows from the absorber chamber 903 to the ink storing portion 901. The ink in the ink storing portion 901 is then replaced with air. Instead, the ink flows into the absorber chamber 903. When an excessive amount of ink flows into the absorber chamber 903, the absorber 907 is fully impregnated with the ink. When the absorber 907 is fully impregnated with the ink, the capillary force thereof is lost. In this case, the ink may leak to the exterior unless the ink tank, the ejection ports in the print head portion, and the like is sealed.
During the distribution of the ink tank configured such that the absorber is housed in one space while the ink is accommodated in the other space, tight sealing is required to prevent the ink from leaking to the exterior. As shown in FIG. 10, the atmospheric communicating port 905 is blocked with a seal 909, and a cap 910 with an elastomer 911 located on an inner surface thereof is installed over the supply port 906.
Means for preventing ink from leaking through the ejection ports in the print head portion is disclosed in, for example, Japanese Patent Laid-Open No. 5-254138. In particular, Japanese Patent Laid-Open No. 5-254138 discloses, for example, a spherical valve, formed of resin or a metal material, is located in the ink channel between the ink tank portion and the print head portion and biased by a spring so that the valve slides to adjust the flow of the ink. However, since the direction in which the valve is opened and closed is parallel to the direction of the flow of the ink, it is difficult to reliably open and close the valve in the sealed channel using a simple operation in a simple structure.
Furthermore, as described above, during distribution, the surrounding environment of the ink tank may vary significantly. Consequently, the pressure inside the ink tank portion may vary markedly. Furthermore, while the ink tank is exposed to distribution conditions over a long period, the air surrounding the ink tank may pass through the wall surface of the ink tank and enter the inside of the ink tank portion. This increases the pressure inside the ink tank portion. When the inside of the ink tank portion is sealed, the internal pressure of the ink tank portion may remove the seal.
In connection with this, Japanese Patent laid-Open No. 8-118676 discloses an ink jet cartridge having a hydrophobic film over an atmospheric communicating port to allow gas to pass through while preventing the flow of liquid. Since gas is allowed to pass through the atmospheric communicating port, the internal air can be discharged according to the pressure of the ink tank portion, enabling the internal pressure to be adjusted. The hydrophobic film needs to be repellent to ink in order to maintain appropriate functions. However, the water repellency has been found to be degraded during a long distribution period in which the hydrophobic film is exposed to the ink or vapor from the ink. Since the distribution period of the ink cartridge may span several years, the ink jet cartridge disadvantageously cannot be adopted until it is recognized whether the water repellency of the hydrophobic film can be maintained over the distribution period.
For the ink tank configured such that the absorber is formed in one space while the ink is accommodated in the other space, an ink jet cartridge having an ink tank portion and a print head portion which are integrally formed may be provided. The ink jet cartridge of this type uses an absorber or the like formed of a sponge to generate negative pressure using a simple structure. When the ink jet cartridge of this type is used, to prevent the possible leakage of the ink caused by an unstable environment during distribution, it is possible to apply a seal tape over the ejection ports in the print head portion.
However, a very adhesive seal tape cannot be adopted for an ink jet printing apparatus adopting an ink jet cartridge having an ink tank portion and a print head portion which are formed as one member. This is because in the ink jet printing apparatus of this type, the ejection ports in the print head portion of the ink jet cartridge are formed to have a very small diameter. If such a seal tape that prevents the possible leakage of the ink through the ejection ports during distribution is applied to the ink jet cartridge, the seal tape needs to have enough adhesiveness to overcome a variation in the internal pressure of the ink tank portion over the distribution period. Thus, in this case, a sufficient amount of paste material needs to be applied to a surface to which the seal tape is applied. However, if the seal tape with the sufficient amount of paste material applied thereto is applied over the ejection ports, the paste material applied to the seal tape application surface may flow into and remain in the ejection ports.
Furthermore, in general, the peripheral area of the ejection ports in the print head portion is not ensured to have high strength. Thus, if such a very adhesive seal tape is applied to the periphery of the ejection ports, the peripheral area of the ejection ports in the print head portion may be deformed when the seal tape is peeled off to allow the use of the ink jet cartridge. Consequently, if the seal tape is applied to the periphery of the ejection ports in the print head portion, the adhesivity cannot be enhanced and is intentionally set low. It is thus difficult to apply the seal tape over the ejection ports in the print head portion to prevent the ink from leaking through the ejection ports to form a sealed structure.
Furthermore, since the seal tape applied over the peripheral area of the ejection ports is not very adhesive, when the pressure inside the ink tank portion increases, the seal tape may be peeled off during distribution, resulting in the leakage of the ink. Thus, since the seal tape is not very adhesive, the ink jet cartridge having the ink tank portion and the print head portion which are formed as one member cannot withstand an unstable environment during distribution. This may result in the leakage of the ink.